In a semiconductor device manufacturing process, management of substrates, such as semiconductor wafers, is usually practiced on a lot basis. For example, when polishing a semiconductor wafer by a polishing apparatus, a plurality of semiconductor wafers (one lot) are housed in a cassette and the cassette is loaded into the polishing apparatus to carry out polishing of the respective wafers.
A semiconductor device is generally manufactured through a plurality of process steps. Thus, in association with the overall process management, a polishing apparatus is not loaded with substrates such as semiconductor wafers for a period of time. During that period, the polishing apparatus enters into the state of idling operation (stand-by operation) in preparation for the next polishing operation. It is a common practice in the time of such idling to supply pure water to a polishing pad (polishing cloth), attached to a polishing table, so as to prevent drying of a surface (polishing surface) of the polishing pad.